1. Field of the Invention
This invention relates to electric systems, and more particularly to motor assemblies.
2. Description of the Related Art
Electric motor driven fans have become an integral part of design for thermal management in electronics. These fans, typically used to cool heat generating components in computer servers, personal computers (PCs) and other electronics, play a critical role in system reliability and longevity. Typical fans have stator windings (“stators”), a single bearing sleeve and a shaft. The stators induce rotor magnets (“rotors”) on a blade assembly armature 130 to rotate, causing air movement through the fan. Various types of fans are used to cool heat generating components, including tube-axial, vane-axial, centrifugal, and blower fans. Regardless of the type of fan used, motor and bearing failures must be minimized to enhance reliability and longevity.
One approach to reduce the impact of motor and bearing failures is described by D. Kim et al. in U.S. Pat. No. 5,920,264. Thermal conditions around the system's cooled parts are monitored to provide a warning should overheating develop. When the temperature around the monitored parts increases past a predetermined level, an alarm sounds from a speaker so that a user can stop the power supplied to the system. Another solution is presented by S. Wrycraft in U.S. Pat. No. 6,011,689 in which an array of fans arranged in parallel cool components in a computer system. Each fan includes an airflow closure member that closes upon failure of the fan. The closure prevents cool air from escaping through the failed fan prior to flowing over a component to be cooled. In this manner, a fan suffering from a failed motor or bearing will not adversely affect the performance of the other fans in the array.
Another solution to reduce the impact of motor and bearing failures is to use multiple fans in series. Unfortunately, this arrangement produces undesirable turbulence noise and increased system impedance if one of the fans should fail. Fan redundancy, either with fans positioned in parallel or series, also reduces the space available for other components and increases system cost due to the increased parts count.
A need continues to exist, therefore, for a motor assembly with increased reliability and longevity without increasing noise, system cost or reducing space available for other components.